1. Field of the Invention
The present invention relates to multilayer impedance components, and more particularly, to multilayer impedance components incorporated in various types of electronic circuits that are used as noise filters.
2. Description of the Related Art
Conventional multilayer impedance components are described, for example, in Japanese Unexamined Patent Application Publication No. 9-7835 and Japanese Unexamined Utility Model Publication No. 6-82822. Each of the multilayer impedance components described in these publications includes a multilayer structure defined by stacking a plurality of coils having different permeabilities. In addition, coil conductor patterns of the coils are electrically connected in series with each other to define a helical coil. In the multilayer impedance component, high impedance is maintained in a wide frequency region from low frequencies to high frequencies such that a noise eliminating frequency band is expanded.
However, in such a multilayer impedance component electrical characteristics change depending upon which of two upper and lower coils having different permeabilities arranged in the multilayer structure is positioned on a mounted-surface side when mounting the impedance element on a printed circuit board.
Additionally, when a pulse signal was input to the multilayer impedance component, research conducted by the inventors of the present invention showed differences in electrical characteristics between when the coil conductor patterns of the high permeability coil section are electrically connected to input and output external electrodes and when the coil conductor patterns of the low permeability coil section are electrically connected to the input and output external electrodes.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a multilayer impedance component having electrical characteristics that do not change regardless of the mounting orientation of the multilayer impedance component, and further provide a multilayer impedance component having excellent electrical characteristics.
According to a first preferred embodiment of the present invention, a multilayer impedance component includes a high permeability coil unit having at least a first winding portion and a third winding portion defined by stacking a plurality of magnetic layers made of a relatively high permeability material and a plurality of coil conductor patterns, and a low permeability coil unit including at least a second winding portion defined by stacking a plurality of magnetic layers made of a relatively low permeability material and a plurality of coil conductor patterns. The high permeability coil unit and the low permeability coil unit are stacked such that the first, second, and third winding portions are electrically connected in series in a sequential manner to define a coil, the first winding portion and the third winding portion of the high-permeability coil unit are connected to input and output external electrodes.
According to a second preferred embodiment of the present invention, a multilayer impedance component includes a first high permeability coil unit including at least a first winding portion defined by stacking a plurality of magnetic layers made of a relatively high permeability material and a plurality of coil conductor patterns, a low permeability coil unit including at least a second winding portion defined by stacking a plurality of magnetic layers made of a relatively low permeability material and a plurality of coil conductor patterns, a second high permeability coil unit including at least a third winding portion defined by stacking a plurality of magnetic layers made of a relatively high permeability material and a plurality of coil conductor patterns. The low permeability coil unit is arranged between the first high permeability coil unit and the second high permeability coil unit such that the first, second, and third winding portions are electrically connected in series in a sequential manner to define a coil, the first winding portion of the first high permeability coil unit and the third winding portion of the second high permeability coil unit are connected to input and output external electrodes.
With the above-described unique arrangement, when a signal of a pulse wave is input to the multilayer impedance component, the signal waveform is blunt in the winding portion of the high permeability coil and thereafter, the waveform is distorted in the winding portion of the low permeability coil. If the coil conductor patterns of the low permeability coil are electrically connected to the input and output external electrodes, the signal waveform is distorted in the low permeability coil and thereafter, the waveform is blunt in the high permeability coil.
When the signal is closer to the pulse wave, the distortion increases. Accordingly, the distortion is greater in a multilayer impedance component having a configuration in which a pulse-wave signal input from input and output external electrodes propagates from a low permeability coil to a high permeability coil. In other words, electrical characteristics are greatly improved in the multilayer impedance component having a configuration in which the coil conductor patterns of the high permeability coil are electrically connected to the input and output external electrodes.
In addition, when the first and third winding portions of the high-permeability coil are connected to the input and output external electrodes, the electrical characteristics are substantially the same regardless of the mounting direction.
Furthermore, an intermediate layer made of a nonmagnetic material is preferably provided between the high permeability coil unit and the low permeability coil unit. Additionally, intermediate layers made of a nonmagnetic material are preferably provided between the first and second high permeability coil units and the low permeability coil unit. The intermediate layer prevents the electromagnetic coupling between magnetic flux generated in the high permeability coil and magnetic flux generated in the low permeability coil. In addition, the intermediate layers prevent mutual diffusion between the materials of the high and low permeability coils, and further prevent warping and cracking from occurring due to the difference between the shrinkage ratios of the materials.